Choosing the best HEPA air purifier for allergies is no simple task, as the market is full of a great deal of variety. Different brands use diverse technologies combined with the HEPA filter to complement its efficacy. Many models tout their ability to remove allergens from the air, but it is important to be informed to make the best decision possible.
Here is how typical HEPA air purifiers work against allergens in the air like pollen, mold and others, and what that means for your specific allergy to pollen, mold, dust mites, etc. Finally we will let you know what you should look for in a HEPA air purifier and what features may be unnecessary to pay for.
Common HEPA and allergy terminology
High-Efficiency Particulate Air filters, commonly known as HEPA filters, were first developed in the 1940s and are perhaps one of the most well-known commercially available technologies for purifying air. They are used in many different areas of daily life, including in aircraft, cars, and vacuum cleaners, as well as both commercial and residential air purifiers. Using a HEPA filter is seen as a standard for some non-residential areas where there is a need to scrub pollutants from the air such as medical facilities like hospitals and laboratories. Many allergy sufferers are advised to use HEPA filters to relieve mild to moderate allergy symptoms.
There are many terms associated with HEPA filters that you may encounter on your search for an air purifier. A basic understanding of these terms will provide a solid foundation of knowledge to build on as you assess how well a device will work on your allergies.
True HEPA: Any filter that can remove 99.97% of the particles that are 0.3 microns or bigger from the air. For the most part, if a manufacturer labels their unit to contain a “HEPA filter” with no qualifiers such as “HEPA-type” or “HEPA-like,” it should meet this standard, though you should check the percentage and particle size is indeed 99.97% at 0.3 microns.
HEPA-like or HEPA-type: A filter which may use similar materials and processes as a true HEPA filter, but may be of varying quality and a lower filtration efficiency standard. This term is not an industry standard.
Allergen: Any substance that is able to cause an allergic reaction. Well-known allergens are dust, mold, pollen, pet dander and dust mite droppings, but can include chemicals in perfumes, from industrial manufacturing, or many other sources. This article will focus on well-known allergens, as a HEPA filter alone cannot deal with gases.
How does a HEPA air purifier work to capture allergens?
The most common allergens are actually tiny proteins that come from living matter, whether from cat and dog dander, dust mites and cockroaches, plant pollen or mold. Allergen-carrying particles vary in size and composition, making some added features within HEPA air purifiers more effective than others.
There are four key ways listed below that HEPA filters capture these allergens, but the main thing to remember is that they are captured on the filter surface:
- Sieving is the process by which particles too large to pass between the extraordinarily small distance separating HEPA fibers become entangled in one or more fibers. This only occurs with particles that are large compared to the fibers.
- Impaction and interception occur when smaller particles collide with a filter fiber and the air passing through the filter is insufficient to move them. Impacted particles strike the surface of the fiber and make a tiny impact crater they cannot escape from. Intercepted particles chemically or physically stick to the surface of a fiber.
- Diffusion is when very tiny particles are buffeted by the air currents in the filter and cannot escape before becoming impacted or intercepted.
After capture by one of these mechanisms, particles can fragment into smaller bits that are then captured by a different mechanism. Note that HEPA traps allergens on a filter surface, and does not permanently remove them.
In order for any of these processes to work correctly, the HEPA filter needs to be functioning properly and moving a large enough volume of air through clean filters.
To determine the efficacy with which an air purifier cleans the air, the market created a standard called the Clean Air Delivery Rate (CADR). CADR describes the amount of air, per minute, to have had all of the particles of any given size removed. Unfortunately, this figure mainly speaks to how fast the air is cleaned, based on filtration efficiency and fan speed, and not necessarily how clean the air is. Note that the substances that cause the allergic reaction – the actual allergens – are tiny chemical components of the particles trapped by the filter, and it is difficult to truly measure how clean the air is based on this number. However, CADR can be a good starting point when assessing the potential performance of a HEPA air purifier.
It is also very important to take care when handling a HEPA filter and be sure that manufacturing guidelines are adhered to. HEPA filters must seal off the dirty air from the clean room, even the smallest hole is a breach in the seal and the dirty air will seek out the path of least resistance, which is right through that hole.
Different types and features of HEPA air purifiers
Standard HEPA only
These are HEPA air purifiers that contain the standard “true-HEPA” filters (99.97% efficiency at 0.3 microns particle size) without other added technologies in the unit. HEPA filters work on allergens as discussed above, where the mesh of fibers undergo impaction, diffusion, sieving and interception to capture pollutants from air passing through.
When it comes to particles, HEPA filters are tested on their ability to capture particles that are 0.3 microns in size. This specific size is chosen because it is the size of a particle most likely to penetrate a HEPA filter by being too small to be sieved and too large to be subject to diffusion. Particles of this specific size are effectively a HEPA filter’s weakness. If a filter can capture a particle of this size, it follows that it can capture particles of most other sizes as well.
Some HEPA filters have electrostatically charged filters, which means the fibers were manufactured to carry a static charge during operation. Some pollutants are attracted to the charge so this addition increases the efficiency of the interception mechanism.
HEPA with UV-C
UV-C is a specific type of ultraviolet light which has mutagenic properties that help HEPA filters by sterilizing biological contaminants that are trapped on the filter. The light eliminates germs by disrupting their DNA and renders them unable to reproduce. Otherwise microbes can feed on the trapped dirt in the filter and multiply, eventually overwhelming the filter and riding the air currents back into the room.
HEPA with carbon filter
The combination of a HEPA filter and an activated carbon filter is seen in many commercially available units. Carbon filters have the ability to grab many airborne chemicals from the air such as volatile organic compounds (VOCs), ozone, and other toxins. This approach uses both the physical particle removal of HEPA and the adsorption capabilities of carbon. Some HEPA filters have carbon on their fibers, but many air purification devices place a carbon bed inside the unit separate from the HEPA filter to capture anything the HEPA cannot.
HEPA with metal oxide catalyst
A catalyst is a substance that can speed up a chemical reaction without itself being used up in that reaction. Air purifiers featuring a metal oxide (usually titanium dioxide) catalyst react with pollutants to vaporize or otherwise decompose them to their component parts. This is a separate mechanism inside a purifier and is usually placed after the HEPA in the flow of air through the device.
HEPA with ionizer technology:
Ionization is the attachment or removal of an electron to something to change its properties. Some purifiers have mechanisms that ionize pollutants. When used in combination with a HEPA filter, particles which pass through or around the filter become ionized which can make them fall to the floor or remain trapped on the filter itself. Particles affected by this technology usually simply fall to and remain on the nearest surface – hopefully, the HEPA medium itself, but sometimes simply other places in the home. Furthermore, the ozone generated by such technologies can cause lung disease and exacerbate allergy symptoms, so be wary when selecting a HEPA filter with this technology.
“HEPA-like” filters that may be conceptually similar to true HEPA, but don’t achieve the same levels of efficiency as true HEPA. The quality of these filters aren’t guaranteed as they not certified to true HEPA standards.
Best types of HEPA air purifier for allergies
Dust, mold, bacteria and pet dander are some of the most common allergens present in our air. In general, they can be removed to a high degree of efficiency (99.97%) by true HEPA filters, though efficiency could be affected by type of allergen. Research has shown that for pet dander, standard HEPA filtration is especially beneficial, while less so on dust mite allergens (Fisk, 2013). When looking at all allergens as a whole, HEPA filtration has been shown in studies to have a moderate improvement on allergy symptoms.
HEPA with UV-C is a good solution for people allergic to mold and mold spores, especially if they’re in a humid environment which is prone to mold growth. UV-C can help reduce some of the mold growth by neutralizing mold spores. An added benefit of this process is that mold growth on the filter itself is less likely. Harmful ozone may also be produced by this process, so it’s necessary to double check that any UV-C unit you choose limits the amount it produces. The California Air Resources board provides a list of certified air cleaning devices for reference, but a good rule of thumb is to look for a carbon stage after the UV stage that will adsorb any ozone.
HEPA and activated carbon combination filters target allergens and odors that might come from pets. Pet dander and smells are both targeted by air purifiers using this technology. However, one consideration for this system is cost. With the continuous shedding of dander, regular filter changes are necessary to maintain effectiveness. Anyone who is allergic to scents or industrial chemicals would need a carbon filter to remove these gases from the air as they often do not travel on particles.
HEPA filters on their own are quite capable of dealing with dust and dust mite related allergies, though filters cleaning a high volume of air, necessary for allergen removal, may be extremely noisy. Depending on the placement of the purifier, sound volume may become a major consideration, especially if used in bedrooms to alleviate nighttime allergy symptoms.
Choosing true HEPA filters without additions eliminates the possibility of producing ozone as a byproduct of ionizers or UV-C addons. Additionally, it reduces the amount of power required to run the unit, as both ionization and UV light production are energy-consuming processes.
Worst types of HEPA air purifier for allergies
Many air pollutants that are allergenic are particulates, which true HEPA filters excel in eliminating.
However, because there are “HEPA-like” filters, and other lower-grade filters made of cheaper materials, simply buying any unit on the market may not be an adequate allergy solution.
Moreover, additional technologies often seen in conjunction with HEPA filters may not be necessary for particulate allergen related issues. HEPA filters equipped with ionizers or activated carbon sheets could be overshooting the mark in terms of symptom management, as they mainly address smells and chemicals passing through the purifier. The production of harmful ozone also should be taken into account before making any purchase, as they can potentially exacerbate allergy symptoms.
Noise, energy, and ease of maintenance
Aside from the simple volume-per-hour air flow through the machine, there are a number of factors which one can use to determine the cost-effectiveness of air purifiers.
Does the unit need to move from room to room? If the answer is yes then in may be worth thinking of getting one that weighs little, or has wheels to facilitate ease of transport. Some HEPA filters are the size of small cars, whereas others are lightweight, portable, and aesthetically pleasing.
If the air purifier needs to run overnight in a bedroom, the noise it produces should be a serious consideration. Certain steps should be taken to ensure that the air purifier selected is quiet or that it can be remotely controlled or scheduled to clean the air during preferred periods. A great convenience enjoyed by many is the ability to control their HEPA filters by their phone, so that when it’s time for bed or upon the arrival of guests, a simple application can quiet the machine down.
The cost of having an air purifier is in part affected by the power it draws. It is important to know exactly what the desired use of the unit is, as having a unit with additional features will mean a greater power consumption. The ability to schedule or fine-tune the operation of the filter will greatly affect power consumption, as you can ensure it runs when it’s most convenient.
Maintenance is vital for all HEPA filter air purifiers to achieve consistently clean air. Replacing filters should be done regularly, with changes being more frequent when being used to clean air with more pollutants. Replacing filters on time is especially important with HEPA filters, to prevent any mold captured on the filter from multiplying.
Some air purifiers, like those with carbon activated sheets, require more frequent maintenance, whereas those featuring ionizer technology will need professional repair, usually back at its manufacturer and rarely for free. UV bulbs can generally be replaced easily, but since they contain toxic mercury vapor extreme care must be taken during replacement and disposal. Devices that use UV LEDs instead of bulbs don’t have this danger.
The best HEPA air purifier for allergies is…
… a simple, straightforward true HEPA filter inside a unit. Of all the technologies, the true HEPA filter should be enough to remove allergens, though you should also consider the right combination of low power consumption, high CADR and acceptable noise level.
The unit should be quiet and portable enough to be convenient, yet effective enough to tackle allergens in the air. You can look for dB levels and weight listed on the package, though not all manufacturers list sound levels. The unit should be placed comfortably in bedrooms as well as living spaces and be simple enough to maintain, requiring easy filter replacements. Furthermore, an air purifier with simply a HEPA filter and without all the other technologies could be more cost effective. The price of an air purifier might increase accordingly with add-ons like carbon or UV technology, though the unit may or may not actually improve allergy conditions within the home. Used with preventative cleaning and the proper steps to ensure a minimal-allergen home, a true HEPA filter may be enough to help your allergies.